Android : Open and save an image in Android Mode and share it on the net

Hi guys for a work at University I need to develop an Android App that open an image in the gallery, apply some filters, and then save image in the gallery in a new folder (better is the image can be shared on facebook/instagram using android built-in sharing api).

Do you know how to do this? I am not new in Processing and I developed a couple of very tiny apps on Eclipse, so I don't have problems using Eclipse, but I don't know how to do this (I am still learning Processing for Android with Eclipse compiler, and I know very little of Android SDK :( )

Thanks a lot to everyone